1. Field of the Invention
The present invention is in the field of medical electronics and more specifically relates to a high-speed online printer/plotter for use in validating the operation of an electrocardiographic data processing system.
2. The Prior Art
In the field of electrocardiology it is known that there are advantages to be able to accrue long term ECG data from a patient while the latter is engaged in normal day-to-day activities. While a "resting" ECG, taken while the patient is in a relaxed state and in a supine position, is useful, there are transient conditions of heart abnormality that occur at non-predicatable and infrequent intervals.
Thus, a patient with a suspected heart problem is monitored for a relatively long period, e.g. 24 to 26 hours or longer by a recorder, carried by the patient, and which records the patient's ECG. The recorder is worn by the patient and may record the ECG on a single track of a cassette type magnetic tape or on dual tracks of a reel-to-reel or tape cartridge. The recorder may be of the type which records the ECG in a memory, either in analog or digital form, and may record all beats of the ECG, or periodic time increments of the ECG, or only that portion of the ECG in which an event of cardiac significance occurs as detected by the patient or by the recorder. One such recorder is that described in U.S. Pat. No. Re. 29,921 and which also provides for the patient to place a code on the tape if the patient should experience some event.
After the monitoring period, the usual practice is to analyze the recorded ECG tape by some form of scanner which in effect "reads" the tape or the stored ECG to extract select meaningful data therefrom. Typical scanners are those described in U.S. Pat. No. 4,006,737 and U.S. Pat. No. Re. 29,921. As described, these scanners operate at 30, 60 or 120 times real time and in real time. Thus, for example, a 24 hour tape can be scanned in as little as 12 minutes. The data may be presented as a print-out of a variety of information, as described in the above-identified patents.
As disclosed therein, the scanner includes an arrhythmia computer whose function is to provide arrhythmia information which may include the number of premature ventricular contractions (VE) or supraventricular ectopic beats (SVE) or both, based on the number per hour or a cumulative total. Additionally such computers may be arranged to provide an indication when the number of VE's or SVE's, or both, exceed a preselected number.
Such arrhythmia computers may also be provided with various controls to permit inclusion of R wave amplitude or width as a criteria for VE beat analysis, as well as other parameters such a paired beats, prematurity, width and the like.
Regardless of the format of arrhythmia analysis, there are instances, totally unrelated to equipment performance in which beats visually recognizable by a trained technician or a cardiologist as arrhythmic are not detected by the scanning equipment. Since the number of arrhythmic beats in an hour or the number per 100 or 1000 heart beats may be of significance to the cardiologist, accurate recognition of those arrhythmic beats not recognized by the scanners may be of importance.
It is thus desirable to provide a reliable method or system by which the high speed arrhythmia analysis of the scanner may be accurately and quickly verified against the actual ECG so that those arrhythmic beats missed, or the normal beats recognized by the scanner as arrhythmic may be correlated, either on a time basis or number of beats basis or both with what actually is present in the ECG.
It is also known in the art that a row of styli extending across a strip of paper moving perpendicularly to the row of styli can be programmed to print or plot data along the strip. This technique lends itself to high-speed printing or plotting when required and where it is permissible to record the data on a relatively long strip of paper such as might be wound on a spool. However, in many situations such a format is not acceptable. In many situations, it is highly desirable to print or plot the data in rows extending across a page, with successive rows arranged one below the other down the page, which is what the present invention does. It is by no means obvious how a row of printing styli can be programmed to record the data in this format. It would appear to require substantial storage capacity and considerable complexity to format the data and to print or plot it in successive rows arranged one below the other down a page. The present invention embodies a novel solution to this problem.
Known prior art plotters do not include any means for entering identifying data onto the plotted chart through the machine, thereby necessitating a separate operation to write the identifying data onto the plotted page. Particularly in the case of medical records, it is essential that the record be properly identified by the patient's name and it is convenient if other vital statistics of the patient are also printed by the machine onto the record.
In some instances, the data to be plotted is accompanied by intermittent time signals. Typically, the data to be plotted is played back from a tape recording and fed to the plotter. An analog-to-digital converter within the plotter is clocked at a constant frequency to convert the data to digital form at a constant sampling rate. If the playback speed of the tape varies, the time between successive played back time signals will also be variable. Therefore, the number of samples of data stored between successive time signals also will vary with the playback speed. Further complicating the situation is the possibility that the time signals may sometimes be omitted.
Normally, it is desirable that the occurrence of a time signal should mark the end of a plotted row of data on the chart. This could be accomplished by starting a new line each time one of the time signals occurs; but, if one of the time signals fails to occur, a problem will result. This situation has, so far as is known, not been the subject of prior work in the art. The present invention includes provision for situations of this type.